The present invention is directed to control of shudder in a power steering system caused by transient lightly damped pressure pulsations in the hydraulic steering fluid, and more particularly to reducing power steering system shudder by damping such fluid pressure pulsations.
Steering shudder is caused by a transient energy spike in the hydraulic steering circuit which oscillates the hydraulic fluid. The time duration of the oscillation (vibration) depends upon the fluid damping. Lightly damped circuits vibrate for a longer time. This invention adds fluid damping to a hydraulic power steering system by creating a leakage across the piston of the steering gear cylinder.
A hydraulic power steering system in accordance with the presently preferred embodiments of the invention includes a steering gear having a cylinder, and a piston slidably disposed in the cylinder to divide the cylinder into first and second cavities on opposed sides of the piston. A pair of turn tubes are coupled to the cylinder for connecting the cylinder cavities to a source of hydraulic fluid. An open fluid leakage path extends between the cylinder cavities or between the turn tubes. This open leakage path is sized to damp fluid pressure fluctuations and thereby reduce fluid-induced shudder in the steering system. In the illustrated embodiments of the invention, the open fluid leakage path may comprise a valve or a passage extending between the turn tubes, a passage in the piston or in the seal between the piston and the gear housing cylinder, or a passage in a banjo block connected across the turn tube inputs to the gear housing.